Ionic conduction in ammonia functionalised closo -dodecaborates MB 12 H 11 NH 3 (M = Li and Na).

Metal hydroborates and their derivatives have been receiving attention as potential solid-state ion conductors for battery applications owing to their impressive electrochemical and mechanical characteristics. However, to date only a fraction of these compounds has been investigated as solid-state electrolytes. Here, MB 12 H 11 NH 3 (M = Li and Na) hydroborates are synthesized and investigated as electrolyte materials for all-solid-state batteries. The room temperature α-NaB 12 H 11 NH 3 was structurally solved in P 2 1 2 1 2 1 ( a = 7.1972(3) Å, b = 9.9225(4) Å, and c = 14.5556(5) Å). It shows a polymorphic structural transition near 140 °C to cubic Fm 3̄ m . LiB 12 H 11 NH 3 and NaB 12 H 11 NH 3 exhibit cationic conductivities of σ (Li + ) = 3.0 × 10 -4 S cm -1 and σ (Na + ) = 1.2 × 10 -4 S cm -1 at 200 °C. Hydration is found to improve ionic conductivity of the hydroborates. It is presumed that modest ionic conductivities could be due to a lack of significant re-orientational dynamics in the crystal structure resulting from the presence of the bulky -NH 3 group in the anion.